1. Field of the Invention
The present invention relates to a stator housing of an electromagnetic clutch and a method for forming a through hole in the stator housing.
2. Description of Related Art
A stator of an electromagnetic clutch includes an exciting coil wound around a spool and a stator for holding the exciting coil. After being received in a receiving portion having a U-shaped cross section, which is formed in the stator housing, the exciting coil is fixed by injecting and molding resin into a space between the exciting coil and the holding portion. In this case, because the receiving portion has an open end at one side in an axial direction thereof, it is necessary to prevent the molded resin with the exciting coil from coming out of the receiving portion.
As methods for preventing the molded resin from coming out, a method using a staked fixing structure shown in FIG. 15 and a method using a dimpling fixing structure shown in FIG. 16 have been proposed. In the staked fixing method, at the closing of a molding die unit before the resin is injected into and molded in the receiving portion 200 for receiving the coil 100, a plurality of staked portions 210 are formed at an opening end of the receiving portion 200 by a staking punch provided on an upper molding die of the die unit. Then, the staked portions 210 are staked to prevent the molded resin 300 from coming out of the receiving portion 200.
On the other hand, in the dimpling fixing method, a dimple portion (concave portion) 220 is formed at an inner peripheral surface of the receiving portion 200, and the resin 300 is injected into the dimple portion 220. Accordingly, the molded resin 300 is restricted from moving in an axial direction and a circumferential direction of the receiving portion 200, thereby being prevented from coming out of the receiving portion 200.
In the staking fixing method, however, because the staking process is added and the staking punch should be changed, the manufacturing cost rises. In the dimpling fixing structure, when the receiving portion 200 is formed by squeezing, the dimple portion 220 having been formed on the wall of the receiving portion 200 in advance is easily broken, and it is difficult to maintain the shape of the dimple portion 220. Therefore, a defective molded resin 300 may be caused. To stabilize the shape of the dimple portion, the number of process steps increases Therefore, the productivity is deteriorated and the manufacturing cost increases.